I'm going to be in DC and I'll have one day all to myself. The next day I'll be doing some sort of touristy stuff with a friend. Last time I was in DC, we did the "walk around the mall" thing and visited the Smithsonian museum of arts and industry.
So there are a lot of places left that I haven't seen. In fact, the choices are rather overwhelming. Anyone have suggestions for what the must-see attractions are? Or for attractions that are a little unusual and not quite overrun with people? (I'll be getting around by Metro and on foot.)